JP5315591B2 - Positive electrode active material and battery - Google Patents

Description

  The present invention relates to a positive electrode active material and a battery. In particular, the present invention relates to a positive electrode active material for a non-aqueous electrolyte secondary battery capable of improving energy density by increasing a charging voltage.

In recent years, with the increase in functionality and performance of portable devices such as notebook computers and mobile phones, the power consumption of the devices has increased. For this reason, a much higher capacity is required for the battery serving as the power source. In addition, from the viewpoints of economy and reduction in size and weight of equipment, a secondary battery having a high energy density has been strongly demanded. Furthermore, there is an increasing demand for an electric vehicle or a hybrid electric vehicle that is actively spread to the general public as a low-pollution vehicle against the background of environmental problems. In response to such demands, non-aqueous secondary batteries, particularly lithium ion secondary batteries, have advantages such as high output and high energy density, and thus are attracting much attention. As a positive electrode active material for a lithium ion secondary battery, LiCoO ₂ or LiNiO ₂ capable of intercalating and deintercalating lithium ions, or a composite oxide partially substituted with a metal element of these lithium-containing transition metal compounds Used. Further, LiMn ₂ O ₄ having a spinel structure or a material obtained by substituting a part of Mn with another element has been developed as an inexpensive material having a high energy density and a high voltage.

  Usually, in a lithium ion secondary battery, a lithium cobaltate is used for the positive electrode and a carbon material is used for the negative electrode, and the operating voltage is used in the range of 2.5V to 4.2V. In the unit cell, the terminal voltage can be increased to 4.2 V largely due to excellent electrochemical stability such as a non-aqueous electrolyte material and a separator.

  By the way, in the conventional lithium ion secondary battery which operates at a maximum of 4.2 V, the positive electrode active material such as lithium cobaltate used in the lithium ion secondary battery only uses about 60% of its theoretical capacity. . When the charging voltage is increased, more lithium is deintercalated and intercalated from the lithium composite oxide, which is the positive electrode active material, so that the capacity can be increased. That is, it is possible in principle to utilize the remaining capacity by increasing the charging voltage. In fact, for example, as disclosed in Patent Document 1, it is known that a high energy density can be realized by setting the voltage during charging to 4.25 V or more.

However, when the charging voltage is increased, there arises a problem that the thermal stability is lowered. Therefore, Li [Ni _x Li _{(1 / 3-2x / 3)} Mn _{(2 / 3-x / 3)} ] O ₂ is used as a positive electrode active material having high thermal stability even when the charging voltage is increased. A Li—Ni—Mn—O-based oxide represented has been proposed (see Non-Patent Document 1). With this positive electrode active material, it has been reported that when X = 1/3, a discharge capacity of 200 mAh / g is obtained in the voltage range of 2.0 to 4.6 V.

  Further, as a positive electrode active material capable of enhancing the stability of the lithium composite oxide, a positive electrode active material containing a large amount of lithium with respect to a metal other than lithium has been proposed (see Patent Document 2).

Electrochemical and Solid-State Letters, 4 (11), A191 (2001) International Publication No. WO03 / 019713 Pamphlet JP 2003-151548 A

  As described above, a battery having a large discharge capacity and excellent stability has been proposed. In recent years, a battery having a larger discharge capacity and excellent charge / discharge characteristics even at a high voltage is obtained. Therefore, realization of a battery that can be used is desired.

  Accordingly, an object of the present invention is to provide a positive electrode active material capable of realizing a large discharge capacity and obtaining excellent charge / discharge characteristics at a high voltage, and a battery using the positive electrode active material.

In order to solve the above-described problems, a first invention of the present invention is a positive electrode active material characterized by containing a lithium composite oxide represented by the following chemical formula.
[Chemical 1]
Li _{1 + a} [Mn _b Co _c Ni _(1-bc) ] _(1-a) O _(2-d)
(Wherein a, b, c and d are 0 <a ≦ 0.15 , 0.5 ≦ b <0.7, 0.2 ≦ c ≦ 0.3 , −0.1 ≦ d ≦ 0, respectively. Within the range of 2.)

A second invention of the present invention comprises a positive electrode, a negative electrode, and an electrolyte,
The positive electrode is a battery characterized by containing a lithium composite oxide represented by the following chemical formula.
[Chemical 1]
Li _{1 + a} [Mn _b Co _c Ni _(1-bc) ] _(1-a) O _(2-d)
(Wherein a, b, c and d are 0 <a ≦ 0.15 , 0.5 ≦ b <0.7, 0.2 ≦ c ≦ 0.3 , −0.1 ≦ d ≦ 0, respectively. Within the range of 2.)

  In this invention, the positive electrode active material contains lithium and transition metal elements of manganese, cobalt, and nickel, and the composition ratio of lithium to the total of the transition metal elements (total of lithium / transition metal elements) is 1 in molar ratio. Therefore, a large electric capacity is obtained at the time of charging, and a certain amount of lithium remains in the crystal structure after charging, so that the stability of the crystal structure is maintained.

  As described above, according to the present invention, since the lithium composite oxide containing manganese, cobalt and nickel is contained, a large capacity and a high potential can be obtained, and a good economic efficiency can be obtained. it can. Since the composition ratio of lithium to the total number of transition metal elements in the lithium composite oxide (total of lithium / transition metal elements) is set to be larger than 1 in molar ratio, the electric capacity during charging can be further improved. At the same time, a certain amount of lithium remains in the crystal structure even after charging, and the stability of the crystal structure can be further improved.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

(1-1) Positive Electrode Active Material A positive electrode active material according to one embodiment of the present invention contains a lithium composite oxide containing lithium and transition metal elements such as manganese, cobalt, and nickel. The object has, for example, a layered structure.

The chemical formula of this lithium composite oxide is represented, for example, by Chemical Formula 1.
[Chemical 1]
Li _{1 + a} [Mn _b Co _c Ni _(1-bc) ] _(1-a) O _(2-d)

  This lithium composite oxide contains excessive lithium, and the composition ratio of lithium to the total of transition metal elements manganese, cobalt, and nickel (total of lithium / transition metal elements) (1 + a) / (1-a) Is greater than 1 in molar ratio, preferably 1 <(1 + a) / (1-a) <1.7, more preferably 1.1 ≦ (1 + a) / (1-a) <1. 7 and even more preferably within the range of 1.2 ≦ (1 + a) / (1−a) ≦ 1.4. By containing excessive lithium, a larger electric capacity can be obtained during charging, and a certain amount of lithium remains in the crystal structure of the lithium composite oxide after charging, and the stability of the crystal structure can be maintained. Because.

  The composition (1 + a) of lithium is, for example, 1 <1 + a <2, preferably 1 <1 + a <1.25, more preferably 1.05 ≦ 1 + a <1.25, and even more preferably 1.1 ≦ a ≦ 1. It is within the range of 15. This is because if it is larger than 1, a large discharge capacity can be obtained, and conversely, if it is 1.25 or more, the crystal structure changes and the discharge capacity decreases. Accordingly, a in [Chemical Formula 1] is, for example, in the range of 0 <a <0.25, preferably 0.05 ≦ a <0.25, and more preferably 0.1 ≦ a ≦ 0.15.

  The manganese composition b is preferably in the range of 0.5 ≦ b <0.7. This is because the discharge capacity decreases when the ratio is less than 0.5, and the cycle characteristics decrease when the ratio is 0.7 or more.

  The cobalt composition c is preferably in the range of 0 ≦ c <(1-b). This is because the charge / discharge capacity is reduced when the value is (1-b) or more.

  The nickel composition (1-bc) is preferably in the range of 0 <(1-bc) ≦ 0.5. This is because if the nickel composition is 0, the structure is unstable, the cycle characteristics of the battery deteriorate, and if the nickel composition exceeds 0.5, the capacity decreases.

  The oxygen composition (2-d) is preferably in the range of 1.8 ≦ (2-d) ≦ 2.2. This is because the structure becomes unstable if it is out of this range.

The positive electrode active material having such a structure can be produced by various methods. For example, lithium carbonate (Li ₂ CO ₃ ), manganese carbonate (MnCO ₃ ), nickel hydroxide (Ni (OH) ₂ ) , Cobalt hydroxide (Co (OH) ₂ ), and the like, if necessary, can be mixed and fired. Specifically, these raw materials are mixed at a predetermined ratio, mixed or pulverized by a ball mill using water or a mixed liquid of water and ethanol as a dispersion medium, and then fired in air or in an oxygen atmosphere. In addition to the materials described above, various carbonates, nitrates, oxalates, phosphates, oxides or hydroxides can be used as raw materials.

(1-2) Configuration of Secondary Battery Next, an example of the configuration of the secondary battery according to the first embodiment of the present invention will be described.

  FIG. 1 is a cross-sectional view showing a configuration example of a secondary battery using a positive electrode active material according to the first embodiment of the present invention. This secondary battery is a so-called coin-type battery. A disc-shaped positive electrode 12 accommodated in the outer can 11 and a disc-shaped negative electrode 14 accommodated in the outer cup 13 are interposed via a separator 15. Are stacked. The interiors of the outer can 11 and the outer cup 13 are filled with an electrolytic solution 16 that is a liquid electrolyte, and the peripheral portions of the outer can 11 and the outer cup 13 are sealed by caulking through an insulating gasket 17.

  The outer can 11 and the outer cup 13 are made of, for example, a metal such as stainless steel or aluminum. The outer can 11 functions as a current collector for the positive electrode 12, and the outer cup 13 functions as a current collector for the negative electrode 14.

  The positive electrode 12 contains, for example, the positive electrode active material according to the first embodiment described above, and is configured with a conductive agent such as carbon black or graphite and a binder such as polyvinylidene fluoride.

The negative electrode 14 includes, for example, lithium metal, a lithium alloy, or any one or more of materials capable of inserting and extracting lithium. Examples of the material capable of inserting and extracting lithium include a carbonaceous material, a metal compound, silicon, a silicon compound, and a conductive polymer, and any one of these or a mixture of two or more thereof is used. Examples of the carbonaceous material include graphite, non-graphitizable carbon, and graphitizable carbon. Examples of the metal compound include oxides such as SnSiO _{3 and} SnO _2. Examples thereof include polyacetylene and polypyrrole. Among these, a carbonaceous material is preferable because a change in crystal structure that occurs during charge / discharge is very small, a high charge / discharge capacity can be obtained, and good cycle characteristics can be obtained. Incidentally, when the negative electrode 14 includes a material capable of inserting and extracting lithium, the negative electrode 14 is configured with a binder such as polyvinylidene fluoride.

  The separator 15 separates the positive electrode 12 and the negative electrode 14 and allows lithium ions to pass through while preventing a short circuit of current due to contact between the two electrodes. The separator 15 is made of, for example, a porous film made of a synthetic resin made of polytetrafluoroethylene, polypropylene, polyethylene, or the like, or a porous film made of an inorganic material such as a ceramic nonwoven fabric. The porous film may be laminated.

The electrolytic solution 16 is obtained by dissolving a lithium salt as an electrolyte salt in a solvent, and exhibits ion conductivity when the lithium salt is ionized. As the lithium salt, LiPF ₆ , LiClO ₄ , LiAsF ₆ , LiBF ₄ , LiCF ₃ SO ₃ or LiN (CF ₃ SO ₂ ) ₂ are suitable, and any one or more of these are mixed. Used.

  Examples of the solvent include propylene carbonate, ethylene carbonate, butylene carbonate, vinylene carbonate, γ-butyrolactone, sulfolane, 1,2-dimethoxyethane, 1,2-diethoxyethane, 2-methyltetrahydrofuran, 3-methyl-1,3- Non-aqueous solvents such as dioxolane, methyl propionate, methyl butyrate, dimethyl carbonate, diethyl carbonate or dipropyl carbonate are preferred, and any one or two or more of these may be used in combination.

  This secondary battery operates as follows. In this secondary battery, when charged, for example, lithium ions are released from the positive electrode 12 and inserted in the negative electrode 14 through the electrolytic solution 16. When the discharge is performed, for example, lithium ions are released from the negative electrode 14 and inserted into the positive electrode 12 through the electrolytic solution 16. Here, since the positive electrode 12 contains a lithium composite oxide containing at least two of the group consisting of manganese, nickel, and cobalt, a large discharge capacity and a high discharge potential can be obtained. In addition, since this lithium composite oxide contains excess lithium, a further excellent discharge capacity can be obtained by improving the charge capacity, and a certain amount of lithium remains on the positive electrode 12 even after charging, and the lithium composite oxide The stability of the crystal structure is further improved, and more excellent charge / discharge cycle characteristics can be obtained.

(1-3) Secondary Battery Manufacturing Method Next, an example of a secondary battery manufacturing method according to the first embodiment of the present invention will be described.

  First, for example, after a positive electrode active material, a conductive agent, and a binder are mixed to prepare a positive electrode mixture, the positive electrode mixture is compression molded into a pellet shape. Thereby, the positive electrode 12 is obtained. In addition to the positive electrode active material, the conductive agent and the binder, a positive electrode mixture was prepared by adding and mixing a solvent such as dimethylformamide or N-methyl-2-pyrrolidone, and the positive electrode mixture was dried. Later, compression molding may be performed. At that time, the positive electrode active material may be used as it is or may be dried, but it reacts when contacted with water, and the function as the positive electrode active material is impaired.

  For example, after the negative electrode active material and a binder are mixed to adjust the negative electrode mixture, the obtained negative electrode mixture is compression molded into a pellet shape. Thereby, the negative electrode 14 is obtained. Also, in addition to the negative electrode active material and the binder, a solvent such as dimethylformamide or N-methyl-2-pyrrolidone is added and mixed to adjust the negative electrode mixture, and the negative electrode mixture is dried and then compressed. The negative electrode 14 may be formed by molding.

  Next, the negative electrode 14 is accommodated in the exterior cup 13, and the gasket 17 is disposed on the peripheral edge of the negative electrode 14. Next, a separator 15 made of a polypropylene porous film or the like is disposed on the negative electrode 14, and a nonaqueous electrolyte is injected into the exterior cup 13, and then the positive electrode 12 is disposed on the separator 15. Finally, covering the negative electrode 14, the separator 15, the positive electrode 12, and the negative electrode cup 13 containing the nonaqueous electrolyte with the outer can 11, the negative electrode cup 13 and the positive electrode can 11 are caulked and fixed via the gasket 17. Thus, a coin-type secondary battery is manufactured.

  As described above, according to the first embodiment, the composition ratio of lithium to the total of transition metal elements (total of lithium / transition metal elements) is set to be larger than 1 in molar ratio. Capacitance and high potential can be obtained, the crystal structure can be stabilized, and charge / discharge cycle characteristics can be improved. Furthermore, the composition ratio of lithium to the total of transition metal elements (total of lithium / transition metal elements) is set to be larger than 1 in terms of molar ratio, so that the electric capacity during charging can be further improved and charging can be performed. Even after the certain amount of lithium remains in the crystal structure, the stability of the crystal structure can be further improved. Therefore, if this positive electrode active material is used, a secondary battery having a large discharge capacity, a high discharge potential, excellent charge / discharge cycle characteristics, and excellent economical efficiency can be obtained.

  Further, the composition of the lithium composite oxide is 0.05 ≦ a <0.25, 0.5 ≦ b <0.65, 0 <c <0.5, −0.1 ≦ d as shown in Chemical Formula 1. When it is within the range of ≦ 0.2, the discharge capacity can be further improved. Therefore, it is possible to obtain a secondary battery that can obtain a larger discharge capacity, a higher discharge potential, and excellent charge / discharge cycle characteristics, as well as excellent economy.

(2) Second Embodiment (2-1) Configuration of Secondary Battery FIG. 2 is a cross-sectional view showing a configuration example of a secondary battery according to the second embodiment of the present invention. This secondary battery is a so-called cylindrical type, in which a pair of strip-like positive electrode 31 and strip-like negative electrode 32 are wound inside a substantially hollow cylindrical battery can 21 via a separator 33. A rotating electrode body 30 is provided. The separator 33 is impregnated with an electrolytic solution that is a liquid electrolyte. The battery can 21 is made of, for example, iron (Fe) plated with nickel (Ni), and has one end closed and the other end open. Inside the battery can 21, a pair of insulating plates 22 and 23 are arranged perpendicular to the winding peripheral surface so as to sandwich the winding electrode body 30.

  At the open end of the battery can 21, a battery lid 24, a safety valve mechanism 25 and a thermal resistance element (PTC element) 26 provided inside the battery lid 24 are interposed via a gasket 27. It is attached by caulking, and the inside of the battery can 21 is sealed. The battery lid 24 is made of the same material as the battery can 21, for example. The safety valve mechanism 25 is electrically connected to the battery lid 24 via the heat sensitive resistance element 26, and the disk plate 25A is reversed when the internal pressure of the battery exceeds a certain level due to an internal short circuit or external heating. Thus, the electrical connection between the battery lid 24 and the wound electrode body 30 is cut off. When the temperature rises, the heat-sensitive resistor element 26 limits the current by increasing the resistance value, and prevents abnormal heat generation due to a large current. The gasket 27 is made of, for example, an insulating material, and asphalt is applied to the surface.

  The wound electrode body 30 is wound around a center pin 34, for example. A positive electrode lead 35 made of aluminum (Al) or the like is connected to the positive electrode 31 of the spirally wound electrode body 30, and a negative electrode lead 36 made of nickel or the like is connected to the negative electrode 32. The positive electrode lead 35 is welded to the safety valve mechanism 25 to be electrically connected to the battery lid 24, and the negative electrode lead 36 is welded to and electrically connected to the battery can 21.

  In this secondary battery, the open circuit voltage in a fully charged state per pair of positive electrode and negative electrode is set to exceed 4.2V, for example, set to 4.4V or more and 4.8V or less.

  FIG. 3 is an enlarged cross-sectional view showing a part of the spirally wound electrode body 30 shown in FIG. Hereinafter, the positive electrode 31, the negative electrode 32, the separator 33, and the electrolyte constituting the secondary battery will be sequentially described with reference to FIG.

(Positive electrode)
The positive electrode 31 has, for example, a structure in which a positive electrode active material layer 31B is provided on both surfaces of a positive electrode current collector 31A having a pair of opposed surfaces. Although not shown, the positive electrode active material layer 31B may be provided only on one surface of the positive electrode current collector 31A. The positive electrode current collector 31A is made of, for example, a metal foil such as an aluminum foil.

  The positive electrode active material layer 31B includes, for example, a positive electrode active material capable of inserting and extracting lithium, and includes a conductive agent such as graphite and a binder such as polyvinylidene fluoride as necessary. It consists of The positive electrode active material is the same as the positive electrode active material described in the first embodiment.

(Negative electrode)
The negative electrode 32 has, for example, a structure in which a negative electrode active material layer 32B is provided on both surfaces of a negative electrode current collector 32A having a pair of opposed surfaces. Although not shown, the negative electrode active material layer 32B may be provided only on one surface of the negative electrode current collector 32A. The negative electrode current collector 32A is made of, for example, a metal foil such as a copper foil.

  The negative electrode active material layer 32B includes, for example, a negative electrode active material that can occlude and release lithium, and includes a binder similar to the positive electrode active material layer 31B as necessary. ing. The negative electrode active material is the same as the negative electrode active material described in the first embodiment.

(Separator, electrolyte)
The configurations of the separator 33 and the electrolyte are the same as those of the separator 15 and the electrolyte described in the first embodiment.

(2-2) Secondary Battery Manufacturing Method Next, an example of a secondary battery manufacturing method according to the second embodiment of the present invention will be described.

  First, for example, a positive electrode active material, a conductive agent, and a binder are mixed to prepare a positive electrode mixture, and the positive electrode mixture is dispersed in a solvent such as N-methyl-2-pyrrolidone to obtain a paste-like material. A positive electrode mixture slurry is prepared. Next, the positive electrode mixture slurry is applied to the positive electrode current collector 31A, the solvent is dried, and the positive electrode active material layer 31B is formed by compression molding using a roll press or the like. Thereby, the positive electrode 31 is obtained.

  Further, for example, a negative electrode active material and a binder are mixed to prepare a negative electrode mixture, and this negative electrode mixture is dispersed in a solvent such as N-methyl-2-pyrrolidone to obtain a paste-like negative electrode mixture slurry Is made. Next, the negative electrode mixture slurry is applied to the negative electrode current collector 32A, the solvent is dried, and the negative electrode active material layer 32B is formed by compression molding using a roll press or the like. Thereby, the negative electrode 32 is obtained.

  Subsequently, the positive electrode lead 35 is attached to the positive electrode current collector 31A by welding or the like, and the negative electrode lead 36 is attached to the negative electrode current collector 32A by welding or the like. After that, the positive electrode 31 and the negative electrode 32 are wound through the separator 33, the front end portion of the positive electrode lead 35 is welded to the safety valve mechanism 25, and the front end portion of the negative electrode lead 36 is welded to the battery can 21. The positive electrode 31 and the negative electrode 32 are sandwiched between a pair of insulating plates 22 and 23 and stored in the battery can 21. After the positive electrode 31 and the negative electrode 32 are accommodated in the battery can 21, the electrolytic solution is injected into the battery can 21 and impregnated in the separator 33. After that, the battery lid 24, the safety valve mechanism 25, and the heat sensitive resistance element 26 are fixed to the opening end portion of the battery can 21 by caulking through the gasket 27. Thereby, the secondary battery shown in FIG. 2 is obtained.

  In this secondary battery, when charged, lithium ions are released from the positive electrode active material layer 31B, and the negative electrode material that can occlude and release lithium contained in the negative electrode active material layer 32B via the electrolytic solution. Occluded. Next, when discharging is performed, lithium ions occluded in the anode material capable of occluding and releasing lithium in the anode active material layer 32B are released and inserted in the cathode active material layer 31B through the electrolytic solution. .

(3) Third Embodiment (3-1) Configuration of Secondary Battery FIG. 4 is a cross-sectional view showing a configuration example of a secondary battery according to the third embodiment of the present invention. In this secondary battery, a battery element 40 to which a positive electrode lead 41 and a negative electrode lead 42 are attached is accommodated in a film-like exterior member 51, and can be reduced in size, weight, and thickness. .

  Each of the positive electrode lead 41 and the negative electrode lead 42 is led out from the inside of the exterior member 51 to the outside, for example, in the same direction. The positive electrode lead 41 and the negative electrode lead 42 are each made of a metal material such as aluminum, copper, nickel, or stainless steel, and each have a thin plate shape or a mesh shape.

  The exterior member 51 is made of, for example, a rectangular aluminum laminated film in which a nylon film, an aluminum foil, and a polyethylene film are bonded together in this order. The exterior member 51 is disposed, for example, so that the polyethylene film side and the battery element 40 face each other, and the outer edge portions are in close contact with each other by fusion or adhesive. An adhesion film 41 for preventing the entry of outside air is inserted between the exterior member 51 and the positive electrode lead 31 and the negative electrode lead 32. The adhesion film 41 is made of a material having adhesion to the positive electrode lead 31 and the negative electrode lead 32, for example, a polyolefin resin such as polyethylene, polypropylene, modified polyethylene, or modified polypropylene.

  The exterior member 51 may be made of a laminated film having another structure, a polymer film such as polypropylene, or a metal film instead of the above-described aluminum laminated film.

  FIG. 5 is a cross-sectional view taken along line VV of battery element 40 shown in FIG. The battery element 40 is obtained by stacking and winding a positive electrode 43 and a negative electrode 44 with a separator 45 and an electrolyte layer 46 interposed therebetween, and the outermost peripheral portion is protected by a protective tape 47.

  The positive electrode 43 has a structure in which a positive electrode active material layer 43B is provided on one or both surfaces of the positive electrode current collector 43A. The negative electrode 44 has a structure in which a negative electrode active material layer 44B is provided on one surface or both surfaces of a negative electrode current collector 44A, and the negative electrode active material layer 44B and the positive electrode active material layer 43B are arranged to face each other. Yes. The configurations of the positive electrode current collector 43A, the positive electrode active material layer 43B, the negative electrode current collector 44A, the negative electrode active material layer 44B, and the separator 45 are respectively the positive electrode current collector 43A and the positive electrode active material layer 43B described in the second embodiment. This is the same as the negative electrode current collector 44A, the negative electrode active material layer 44B, and the separator 33.

  The electrolyte layer 46 includes an electrolytic solution and a polymer compound serving as a holding body that holds the electrolytic solution, and has a so-called gel shape. The gel electrolyte layer 46 is preferable because high ion conductivity can be obtained and battery leakage can be prevented. The configuration of the electrolytic solution (that is, the solvent and the electrolyte salt) is the same as that of the secondary battery according to the second embodiment. Examples of the polymer compound include polyacrylonitrile, polyvinylidene fluoride, a copolymer of vinylidene fluoride and hexafluoropropylene, polytetrafluoroethylene, polyhexafluoropropylene, polyethylene oxide, polypropylene oxide, polyphosphazene, and polysiloxane. , Polyvinyl acetate, polyvinyl alcohol, polymethyl methacrylate, polyacrylic acid, polymethacrylic acid, styrene-butadiene rubber, nitrile-butadiene rubber, polystyrene or polycarbonate. In particular, polyacrylonitrile, polyvinylidene fluoride, polyhexafluoropropylene or polyethylene oxide is preferable from the viewpoint of electrochemical stability.

(3-2) Method for Manufacturing Secondary Battery Next, an example of a method for manufacturing a secondary battery according to the third embodiment of the present invention will be described.

  First, a precursor solution containing a solvent, an electrolyte salt, a polymer compound, and a mixed solvent is applied to each of the positive electrode 43 and the negative electrode 44, and the mixed solvent is volatilized to form a gel electrolyte layer 46. After that, the positive electrode lead 41 is attached to the end of the positive electrode current collector 43A by welding, and the negative electrode lead 42 is attached to the end of the negative electrode current collector 44A by welding. Next, the positive electrode 43 and the negative electrode 44 on which the gel electrolyte layer 46 is formed are laminated through a separator 45 to form a laminated body, and then the laminated body is wound in the longitudinal direction, and a protective tape is formed on the outermost peripheral portion. 47 is bonded to form the battery element 40. Finally, for example, the battery element 40 is sandwiched between the exterior members 51, and the outer edges of the exterior members 51 are sealed and sealed by thermal fusion or the like. At that time, an adhesion film 52 is inserted between the positive electrode lead 41 and the negative electrode lead 42 and the exterior member 51. Thereby, the secondary battery shown in FIGS. 4 and 5 is obtained.

  Further, this secondary battery may be manufactured as follows. First, the positive electrode 43 and the negative electrode 44 are prepared as described above, and after the positive electrode lead 41 and the negative electrode lead 42 are attached to the positive electrode 43 and the negative electrode 44, the positive electrode 43 and the negative electrode 44 are stacked via the separator 45 and wound. The protective tape 47 is adhered to the outermost peripheral portion to form a wound body that is a precursor of the battery element 40. Next, the wound body is sandwiched between the exterior members 51, and the outer peripheral edge portion excluding one side is heat-sealed to form a bag shape, and is stored inside the exterior member 51. Subsequently, an electrolyte composition including a solvent, an electrolyte salt, a monomer that is a raw material of the polymer compound, a polymerization initiator, and other materials such as a polymerization inhibitor as necessary is prepared, and the exterior member 51 is injected into the interior.

  After injecting the electrolyte composition, the opening of the exterior member 51 is heat-sealed and sealed in a vacuum atmosphere. Next, the gelled electrolyte layer 46 is formed by applying heat to polymerize the monomer to obtain a polymer compound. Thus, the secondary battery shown in FIG. 4 is obtained.

  EXAMPLES Hereinafter, the present invention will be specifically described with reference to examples. However, the present invention is not limited to these examples.

(Examples 1-1 to 1-4, Reference Example 1-5 )
First, a ball mill using lithium carbonate (Li ₂ CO ₃ ), manganese carbonate (MnCO ₃ ), nickel hydroxide (Ni (OH) ₂ ), and cobalt hydroxide (Co (OH) ₂ ) as a dispersion medium. Thoroughly mixed and ground. At that time, the blending molar ratio of the raw materials was changed so that the composition of the obtained lithium composite oxide was as shown in Table 1. Next, the obtained mixture was baked in air at 850 ° C. for 12 hours, and lithium composite oxide Li _{(1 + a)} [Mn _0.6 Co _0.2 Ni _0.2 ] _(1-a) O ₂ having the composition shown in Table 1 was obtained. Was synthesized.

(Comparative Examples 1-1, 1-2)
The lithium composite oxide Li _{(1 + a)} [Mn _0.6 Co] having the composition shown in Table 1 was carried out in the same manner as in Examples 1-1 to 1-4 and Reference Example 1-5 except for the mixing molar ratio of the raw materials. the _{0.2 Ni 0.2] (1-a} ) O 2 was synthesized.

Table 1 shows the composition of the lithium composite oxide according to Examples 1-1 to 1-4, Reference Example 1-5, and Comparative Examples 1-1 and 1-2.

With respect to the obtained lithium composite oxides of Examples 1-1 to 1-4, Reference Example 1-5, and Comparative Examples 1-1 and 1-2, powder X-ray diffraction patterns were measured. A rotating counter cathode type Rigaku RINT2500 was used for the X-ray diffractometer. This X-ray diffractometer is equipped with a vertical standard radius of 185 mm as a goniometer, and without using a filter such as a Kβ filter, the X-ray diffractometer is made monochromatic by combining a wave height analyzer and a counter monochromator. The specific X-ray is detected by a scintillation counter. The measurement uses CuKα (40 kV, 100 mA) as specific X-rays, the incident angle DS with respect to the sample surface and the angle RS formed by the diffraction lines with respect to the sample surface are each 1 °, and the width SS of the incident slit is 0.15 mm. (Scanning range 2θ = 10 ° to 90 °, scanning speed 4 ° / min).

FIG. 6 shows the X-ray diffraction patterns of the lithium composite oxides of Examples 1-1 to 1-4, Reference Example 1-5, and Comparative Examples 1-1 and 1-2. All of these lithium composite oxides were found to have a layered structure. In these lithium composite oxides, a slight peak indicating impurities was observed at around 21 °, but the peak of Comparative Example 1-1 was slightly larger.

Further, using the lithium composite oxides of Examples 1-1 to 1-4, Reference Example 1-5, and Comparative Examples 1-1 and 1-2, a coin-type secondary battery as shown in FIG. 1 was produced. Then, the characteristics of the positive electrode active material were evaluated by examining the charge / discharge characteristics.

The positive electrode 12 of the secondary battery was produced as follows. First, the synthesized lithium composite oxide Li _{(1 + a)} [Mn _0.6 Co _0.2 Ni _0.2 ] _(1-a) O ₂ is dried to form a positive electrode active material, and this positive electrode active material is combined with graphite as a conductive agent. The paste was mixed with polyvinylidene fluoride (Aldrich # 1300) as a binder using N-methyl-2-pyrrolidone as a solvent to obtain a paste-like positive electrode mixture. The ratio of the positive electrode active material, graphite, and polyvinylidene fluoride was 85% by mass of the positive electrode active material, 10% by mass of acetylene black, and 5% by mass of polyvinylidene fluoride. Next, 60 mg of this positive electrode mixture was pelletized together with a net-like current collector made of aluminum, and dried at 100 ° C. for 1 hour in a dry argon (Ar) gas stream to obtain a positive electrode 12.

A lithium metal plate punched into a disk shape is used for the negative electrode 14, a porous film made of polypropylene is used for the separator 15, and ethylene carbonate and dimethyl carbonate are mixed at a volume ratio of 1: 1 in the electrolyte solution 16. the LiPF ₆ as a lithium salt were used as dissolved at a concentration of 1 mol / l in a solvent. The size of the secondary battery was 20 mm in diameter and 1.6 mm in height.

Moreover, charging / discharging was performed as follows. First, constant current charging was performed at a constant current of 1 mA until the battery voltage reached 4.6 V, and then constant voltage charging was performed at a constant voltage of 4.6 V until the current became 0.3 mA / cm ² or less. Next, constant current discharge was performed at a constant current of 0.5 mA until the battery voltage reached 2.0V. At that time, this charging / discharging was performed in a normal temperature environment (23 ° C.).

FIG. 7 shows a charge / discharge curve of the secondary battery using the lithium composite oxide according to Example 1-3. FIG. 8 shows values of a and discharges in the first cycle in secondary batteries using lithium composite oxides according to Examples 1-1 to 1-4, Reference Example 1-5 and Comparative Examples 1-1 and 1-2. The relationship with capacity is shown. In FIG. 7, the solid line is the charge / discharge curve of the first cycle, and the short broken line is the charge / discharge curve of the second cycle.

As can be seen from FIG. 8, the discharge capacity increases as a in the lithium composite oxide Li _{(1 + a)} [Mn _0.6 Co _0.2 Ni _0.2 ] _(1-a) O ₂ increases from 0. When the value of .13 was reached, the maximum value was observed, and when a exceeded 0.13, the value decreased. It is considered that the reason why the discharge capacity decreases when a is made too large is that the lithium content exceeds the amount necessary for structural stabilization and the structure becomes unstable.

Accordingly, a in the lithium composite oxide Li _{(1 + a)} [Mn _0.6 Co _0.2 Ni _0.2 ] _(1-a) O ₂ is preferably 0 <a <0.25, more preferably 0.05 ≦ a. It has been found that a larger discharge capacity can be obtained if it is within the range of <0.25, more preferably 0.1 ≦ a ≦ 0.15. That is, the molar composition ratio of lithium to the total number of transition metal elements (total of lithium / transition metal elements) (1 + a) / (1-a) is preferably 1 <(1 + a) / (1-a) <1.7. More preferably, 1.1 ≦ (1 + a) / (1-a) <1.7, and even more preferably 1.2 ≦ (1 + a) / (1-a) ≦ 1.4. It was found that a larger discharge capacity can be obtained.

(Examples 2-5 to 2-7, Reference Examples 2-1 to 2-4, 2-8 )
Examples 1-1 to 1 described above except that the compounding molar ratio of the raw materials is changed to synthesize lithium composite oxide Li _1.13 [Mn _0.6 Co _c Ni _0.4-c ] _0.87 O ₂ having the composition shown in Table 2. -4 and Reference Example 1-5 were all carried out in the same manner to produce a coin-type secondary battery. Next, charging and discharging were performed in the same manner as in Examples 1-1 to 1-4 and Reference Example 1-5 , and battery characteristics were evaluated. The results are shown in Table 2 and FIG.

(Comparative Example 2-1)
Examples 2-5 to 2-7 described above except that the compounding molar ratio of the raw materials was changed to synthesize lithium composite oxide Li _1.13 [Mn _0.6 Co _0.4 ] _0.87 O ₂ having the composition shown in Table 2. A coin-type secondary battery was fabricated in the same manner as in Examples 2-1 to 2-4 and 2-8 . Next, charging and discharging were performed in the same manner as in Examples 1-1 to 1-4 and Reference Example 1-5 , and battery characteristics were evaluated. The results are shown in Table 2 and FIG.

Table 2 shows the evaluation results of the battery characteristics of Examples 2-5 to 2-7, Reference Examples 2-1 to 2-4, 2-8, and Comparative Example 2-1 . The charge / discharge efficiency shown in Table 2 is calculated by the following formula.
[Formula 1]
Charging / discharging efficiency = (discharge capacity / charge capacity) × 100

FIG. 9 shows the relationship between the composition of cobalt and the charge / discharge capacity in the secondary batteries according to Examples 2-5 to 2-7, Reference Examples 2-1 to 2-4, 2-8, and Comparative Example 2-1. . As can be seen from FIG. 9, when the lithium composition (1 + a) is 1.13 and the manganese composition b in the transition metal component is 0.6, the cobalt composition c is 0 <c ≦ A high charge / discharge capacity can be obtained even when changing within the range of 0.35, whereas when the cobalt composition c is 0.4, that is, in the chemical formula shown in [Chemical Formula 1] When the composition (1-bc) was 0, the battery capacity tended to decrease.

  In addition, the charge / discharge capacity increased as the cobalt composition c increased from 0, reached a maximum when the composition c was 0.3, and decreased rapidly when the composition c exceeded 0.3.

As described above, the cobalt composition c in [Chemical Formula 1] is preferably in the range of 0 < c <0.4, that is, 0 ≦ c <(1-b), and 0 < c ≦ 0.35, that is, 0 <. More preferably within the range of c ≦ (0.95-b), and even more preferably within the range of 0 < c ≦ 0.3, that is, 0 ≦ c ≦ (0.9−b). I understood.

(Example 3-1)
Except that raw material by varying the molar amounts synthesize lithium composite oxide _{Li 1.13 [Mn 0.5 Co 0.25 Ni} 0.25] 0.87 O 2 is in the above Examples 1-1 to 1-4, Reference Example 1-5 In the same manner, a coin-type secondary battery was produced. Subsequently, the battery characteristics were evaluated by repeating the charge and discharge in the same manner as in Examples 1-1 to 1-4 and Reference Example 1-5 . The results are shown in Table 3.

(Example 3-2)
Except that raw material by varying the molar amounts synthesize lithium composite oxide _{Li 1.13 [Mn 0.65 Co 0.20 Ni} 0.15] 0.87 O 2 is in the above Examples 1-1 to 1-4, Reference Example 1-5 In the same manner, a coin-type secondary battery was produced. Subsequently, the battery characteristics were evaluated by repeating the charge and discharge in the same manner as in Examples 1-1 to 1-4 and Reference Example 1-5 . The results are shown in Table 3.

(Comparative Example 3-1)
Except that raw material by varying the molar amounts synthesize lithium composite oxide _{Li 1.13 [Mn 0.45 Co 0.35 Ni} 0.20] 0.87 O 2 is in the above Examples 1-1 to 1-4, Reference Example 1-5 In the same manner, a coin-type secondary battery was produced. Subsequently, the battery characteristics were evaluated by repeating the charge and discharge in the same manner as in Examples 1-1 to 1-4 and Reference Example 1-5 . The results are shown in Table 3.

(Comparative Example 3-2)
Except for synthesizing lithium composite oxide Li _1.13 [Mn _0.7 Co _0.3 Ni _0.1 ] _0.87 O ₂ by changing the mixing molar ratio of the raw materials, the above-described Examples 1-1 to 1-4, Reference Example 1-5 and In the same manner, a coin-type secondary battery was produced. Subsequently, the battery characteristics were evaluated by repeating the charge and discharge in the same manner as in Examples 1-1 to 1-4 and Reference Example 1-5 . The results are shown in Table 3.

Table 3 shows the evaluation results of the battery characteristics of the secondary batteries according to Examples 2-6, 3-1, 3-2 and Comparative Examples 3-1, 3-2. In addition, the capacity maintenance rate at 30 cycles in Table 3 is calculated by the following formula.
[Formula 2]
Capacity maintenance rate at 30 cycles = (discharge capacity at 30 cycles / discharge capacity at 1 cycle) × 100

  As can be seen from Table 3, in the lithium composite oxide represented by [Chemical Formula 1], when the manganese composition b is in the range of 0.5 ≦ b <0.7, high charge / discharge capacity and good cycle characteristics are obtained. On the other hand, when b <0.5, the discharge capacity is remarkably lowered, and when 0.7 ≦ b, a higher initial capacity is obtained, but the capacity retention rate after cycling tends to be remarkably lowered. It was.

  As described above, the manganese composition b in [Chemical Formula 1] is preferably in the range of 0.5 ≦ b <0.7, and more preferably in the range of 0.5 ≦ b ≦ 0.65. I understood that.

(Test Examples 1-9)
In the secondary battery using Li _1.13 [Mn _0.6 Co _0.2 Ni _0.2 ] _0.87 O ₂ synthesized in Example 2-5 as the positive electrode active material, the charging voltage was changed within the range of 4.25V to 5.1V. The charge / discharge capacity was measured. The results are shown in Table 4 and FIG.

Table 4 shows the measurement results of the charge / discharge capacity of the secondary batteries according to Test Examples 1 to 9.

  FIG. 10 shows the relationship between the charging voltage and charging / discharging capacity of the secondary battery according to Test Examples 1-9. As can be seen from FIG. 10 and Table 4, when the charging voltage is in the range of 4.2 V to 4.4, the charging / discharging capacity gradually increases as the charging voltage is increased, but the charging voltage is not sufficient, but the charging voltage is 4.4 V. Above this, the charge / discharge capacity increased remarkably, and when the charge voltage exceeded 4.8V, the increase in charge capacity became small, and the discharge capacity did not increase, and when it exceeded 4.95V, a tendency to begin to decrease was observed. .

  As described above, it has been found that the positive electrode active material having the composition shown in [Chemical Formula 1] can sufficiently exert its effect when the charging voltage is in the range of 4.4 V or more and 4.8 V or less.

  In the above-described examples, the composition of the lithium composite oxide has been described by way of an example. However, the same effect can be obtained with other compositions as long as it is within the range of the composition described in the above-described embodiment. be able to.

  Although the embodiments and examples of the present invention have been specifically described above, the present invention is not limited to the above-described embodiments and examples, and various modifications based on the technical idea of the present invention are possible. It is.

  For example, the numerical values given in the above-described embodiments and examples are merely examples, and different numerical values may be used as necessary.

  The configurations of the above-described embodiments and examples can be combined with each other without departing from the gist of the present invention.

In the above-described embodiments and examples, the case where the positive electrode active material includes the lithium composite oxide having the above-described composition has been described. In addition to the lithium composite oxide, LiCoO ₂ , LiNiO ₂ , LiMnO _2, or LiMn Other lithium composite oxides such as ₂ O ₄ , lithium sulfide, lithium-containing phosphates such as LiMn _x Fe _y PO ₄ , or polymer materials may be mixed.

  Furthermore, in the above-described embodiments and examples, the case where an electrolytic solution that is a liquid electrolyte is used as an electrolyte or the case where a gel electrolyte in which an electrolytic solution is held in a polymer compound is used as an electrolyte has been described. An electrolyte may be used. Other electrolytes include, for example, an organic solid electrolyte in which an electrolyte salt is dispersed in a polymer compound having ionic conductivity, an inorganic solid electrolyte made of ionic conductive ceramics, ionic conductive glass, ionic crystals, or the like. Examples thereof include a mixture of an inorganic solid electrolyte and an electrolytic solution, or a mixture of these inorganic solid electrolyte and a gel electrolyte or an organic solid electrolyte.

  Furthermore, in the above-described embodiments and examples, the coin-type secondary battery has been specifically described, but the present invention is a secondary battery having another shape such as a button type or a square type, or a winding structure. The present invention can be similarly applied to secondary batteries having other structures.

  Moreover, although the above-mentioned embodiment and Example demonstrated the case where the positive electrode active material of this invention was used for a secondary battery, it can apply similarly to other batteries, such as a primary battery.

It is sectional drawing which shows the example of 1 structure of the secondary battery by 1st Embodiment of this invention. It is sectional drawing which shows one structural example of the secondary battery by the 2nd Embodiment of this invention. It is sectional drawing which expands and shows a part of winding electrode body shown in FIG. It is sectional drawing which shows the example of 1 structure of the secondary battery by 3rd Embodiment of this invention. It is sectional drawing along the VV line of the battery element shown in FIG. It is a characteristic view showing the X-ray-diffraction pattern of the positive electrode active material by Examples 1-1 to 1-4, Reference Example 1-5, and Comparative Examples 1-1 and 1-2. It is a characteristic view showing the charging / discharging curve of the secondary battery using the positive electrode active material by Example 1-3. The relationship between the value of a in the secondary battery using the positive electrode active material according to Examples 1-1 to 1-4, Reference Example 1-5, and Comparative Examples 1-1 and 1-2 and the discharge capacity in the first cycle is shown. FIG. It is a characteristic view showing the relationship between the composition of cobalt and the charge / discharge capacity in the secondary batteries according to Examples 2-5 to 2-7, Reference Examples 2-1 to 2-4, 2-8, and Comparative Example 2-1 . . It is a characteristic view which shows the relationship between the charging voltage and charging / discharging capacity | capacitance of the secondary battery by Test Examples 1-9.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 11 ... Outer can, 12, 31 ... Positive electrode, 13 ... Outer cup, 14, 32 ... Negative electrode, 15, 33, 45 ... Separator, 16 ... Electrolyte solution, 17 ... Gasket, 21 ... battery can, 22,23 ... insulating plate, 24 ... battery cover, 25 ... safety valve mechanism, 25a ... disc plate, 26 ... heat sensitive resistance element, 27 ... Gasket, 30 ... Winding electrode body, 31a, 43a ... Positive electrode current collector, 31B, 43b ... Positive electrode active material layer, 32a, 44a ... Negative electrode current collector, 32b, 44b ... negative electrode active material layer, 34 ... center pin, 35, 41 ... positive electrode lead, 36, 42 ... negative electrode lead, 40 ... positive electrode element, 47 ... protective tape, 51 ...・ Exterior member, 52 ... Adhesion film

Claims (2)

A positive electrode active material comprising a lithium composite oxide represented by the following chemical formula.
[Chemical 1]
Li _{1 + a} [Mn _b Co _c Ni _(1-bc) ] _(1-a) O _(2-d)
(Wherein a, b, c and d are 0 <a ≦ 0.15, 0.5 ≦ b <0.7, 0.2 ≦ c ≦ 0.3, −0.1 ≦ d ≦ 0, respectively. Within the range of 2.) A positive electrode, a negative electrode, and an electrolyte;
The positive electrode contains a lithium composite oxide represented by the following chemical formula.
[Chemical 1]
Li _{1 + a} [Mn _b Co _c Ni _(1-bc) ] _(1-a) O _(2-d)
(Wherein a, b, c and d are 0 <a ≦ 0.15, 0.5 ≦ b <0.7, 0.2 ≦ c ≦ 0.3, −0.1 ≦ d ≦ 0, respectively. Within the range of 2.)

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